I'm getting the One S for sure. I have decided the space that it'll save me is worth it -- 40% smaller is almost half the size w/o the brick. I just have a few questions which won't change whether I get it, but will change whether I trade in my Xbox Elite.
Does it have a hybrid HD (SSHD) like the Elite console?
Can I swap the hard drive easily? On the ps4 I can get a laptop HD and put it in my console for more space.
Will the current games record in 4k or 1080p or will it be whatever Xbox had it? For example, BO3 isn't full 1080p on Xbox... will it now be 1080p with the system? My monitor and tv are already 1080p screens.
Just get an external hard drive. Much better proposition. My primary Xbox One has 8.5 TB (2 4 TB and the internal 500 GB). And you can move the external drives between Xbox One systems. With the PS4, you have no external option and you have to replace the internal meaning you're not gaining the full amount. So for example, if you replace the 500 GB with a 1 TB, you're only netting 500 GB because you took out the 500 GB. Also, there's a limit to how much storage you can put in since it must be a 2.5 inch internal type (9.5mm or slimmer). You can't get 4 TB 2.5" drives that are 9.5 mm or slimmer.
The Xbox One S will upscale all games to 4K. However, it's up to you to decide whether you like the quality of the Xbox One S scaler or prefer your 4K TV's upscaler. You really have to play with both to see what scaling you prefer. I would assume the AMD scaler would do better and have less latency than your TV scaler. The Xbox One already scales content to 1080P. No one knows if the Xbox One S will have better scaling to 1080P than the original Xbox One.
You really need a HDR TV to fully appreciate. That's the big differentiator for the One S. You're going from 16 million colors for a regular TV/PC monitor to 1 billion colors for an HDR TV. As well as greater contrast. really black blacks and really white whites. so far 3 games will support HDR (Gears of War 4, Forza Horizon 3, and Scalebound). Too bad the Xbox One S doesn't support Dolby Vision. Dolby Vision is 12-bit color so it goes up to 68 billion colors (4096 shades per color) versus HDR10 which is 10-bit color which gets you 1 billion colors (1024 shades per color).
The funny thing is it will be hard for Microsoft to advertise HDR because most people will be viewing movies and screenshots on their PC monitors, tablets, and phones which cannot display HDR. It's like telling people how great color TV is but they're watching the shows on a black and white TV.